1. Field
Embodiments disclosed herein relate to optical components. In particular, some embodiments described herein relate to wavelength lockers suitable for use with tunable lasers.
2. Related Technology
Laser frequency monitoring and locking is an essential technology in a variety of diverse applications, including telecommunications, medical devices, and optical computing. For example, optimization of a dense wavelength division multiplexing (DWDM) system requires precise control and accurate tuning of the frequencies transmitted along an optical fiber by a laser. In DWDM systems, each laser signal is tuned in frequency to a discrete channel, allowing a plurality of signals to be simultaneously transmitted in a single fiber and therefore enabling a large volume of information to be transmitted through a single fiber. Each of these lasers may be locked to a wavelength locker to ensure that it remains tuned to its proper channel, regardless of any environmental or systematic factors. The communication channels are defined on a grid with equal frequency spacing in a band at approximately 194 THz (the ITU grid).
A wavelength locker provides a calibrated reference for determining the wavelength deviation of a laser output from a desired wavelength (e.g., an ITU communications channel), which is used to tune the laser wavelength back to the desired wavelength. Thus, wavelength lockers are critical to optical communication systems because they enable more closely-spaced channels, thereby increasing the bandwidth of the system.
For optical communication systems where the communications channels must be spaced equally apart in frequency, an interferometric optical element, such as a Fabry-Perot (FP) etalon, is commonly used as the reference element of a wavelength locker. An FP etalon is composed of two partially-reflecting mirrors that are substantially parallel and separated by a gap. The wavelength locker matches the Free Spectral Range (FSR) of the etalon to the frequency spacing of the ITU grid such that the FP etalon acts as a reference to indicate where the ITU channels are located.
In some optical communication systems, gridless tuning may be desirable. Gridless tuning enables a user or operator to tune an optical source to intermediate wavelengths within the ITU grid, as well as wavelengths beyond the ITU grid and/or the wavelengths of the ITU grid itself. Gridless tuning may therefore enable a user or operator to continuously tune an optical source to any wavelength in a wavelength range that may include one or more ITU grid wavelengths and/or other wavelengths of interest. One approach to achieving gridless tuning has been the use of a specialized double etalon assembly having two resonators disposed in a side-by-side configuration such that the etalons are offset by a specified fraction of their respective FSR. However, the required difference in thickness (approximately 1 or 2 micrometers) between the two etalons can create manufacturing difficulties. Furthermore, crosstalk issues between the two etalons may arise if the etalons are not separated a sufficient distance apart from one another, and the required gap between the two etalons increases the overall size of the wavelength locker.
Another approach to achieving gridless tuning has been the use of a single etalon with a thermoelectric cooler (TEC) which can tune the optical source by adjusting the operating temperature of the optical source. Upon achieving the desired wavelength, the TEC may maintain its temperature to lock the wavelength of the optical source. However, use of temperature-controlled tuning may be inaccurate and mechanically unstable, and may require high power consumption.
The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced.